This invention relates in general to Local Area Networks (LANs) and, more particularly, to radio LANs which operate in a spread spectrum environment.
Conventional wire-based LAN systems employ extensive fixed cabling to interconnect the multiple stations which form the networked system. The installation of such fixed cabling is difficult enough when performed concurrently with new building construction and is even more problematic when an existing structure must be retrofitted. In the resultant LAN using fixed cabling, the networked stations are constrained to installation at fixed locations which are dependent on such cabling.
To address these concerns and limitations, radio LANs have been developed which utilize radio links rather than cable to interconnect the network stations. Unfortunately, radio based LANs encounter another set of problems unique to the indoor radio environment. For example, radio LANs are susceptible to multi-path fading which can interfere with interstation communication. To alleviate the problem of multi-path fading, radio based LANs have been developed which employ spread spectrum transmitting and receiving technology.
FIG. 1 shows a conventional radio LAN including stations 1, 2, 3 . . . N which are interconnected by a radio link. These stations each include radio transmitting and radio receiving portions (not shown). A LAN station typically transmits information in frames such as frame 10 shown in FIG. 2. Frame 10 includes a preamble 12, a start delimiter 14 designated SD, a network ID number 16 designated NWID, the user data 18 and an end delimiter 20 designated ED. In the radio LAN environment, there is a need for synchronization during the reception of the frame in order to recover the user data. To facilitate such synchronization, the start delimiter SD is transmitted preceding the synchronization sensitive part of the frame. More specifically, symbol synchronization is required to receive the network identification number NWID and the user data.
In addition to the need for symbol synchronization described above, there is also a need to transmit a firm point to specify the end of a frame. The end delimiter ED is transmitted to perform this function. It is thus seen that in frame 10 of FIG. 2, the start delimiter SD and the end delimiter ED specify the beginning and the end, respectively, of the information for which synchronization is required.
It is also desirable that the start delimiter and the end delimiter take a minimum number of symbols. Conventional delimiter protocols include using a fixed data pattern (flag) and applying zero insertion to prevent illegal flag detection in the user data part of the frame. Unfortunately, such delimiter protocols undesirably add to the length of the frame and therefore result in extra system overhead. Increasing the system overhead in this manner significantly decreases network performance of the radio LAN.